Japanese Patent No. 2,990,646 (JP-A 8-199070) discloses a curable composition comprising a linear perfluoropolyether compound containing at least two alkenyl groups per molecule and having a perfluoropolyether structure in its backbone, an organosilicon compound having at least two H—SiOSiO structures per molecule, and a hydrosilylation catalyst, which cures into a product having a good profile of heat resistance, chemical resistance, solvent resistance, water repellency, oil repellency and weatherability.
These perfluoropolyether rubber compositions perform well in most applications. However, their acid resistance is short in those applications requiring chemical resistance such as sealants in semiconductor manufacturing units, sealants and potting materials for use with engine oil, and sealants and potting materials for use in engine exhaust parts. There is a need for perfluoropolyether rubber or gel compositions which are improved in oil resistance and chemical resistance, and especially acid resistance.
JP-A 2000-248166 discloses a curable fluoropolyether base rubber composition comprising a linear fluoropolyether compound having at least two alkenyl groups, an organosilicon compound having at least two SiH groups, a hydrosilylation catalyst, and surface-hydrophobicized microparticulate silica having a specific surface area of at least 50 m2/g and a nitrogen atom content of 500-5,000 ppm.